Development and Density of Stomata on Fruit Surfaces during Fruit Growth in Nectarine

Abstract

This work was undertaken to clarify the development and density of stomata on fruit surfaces and diurnal changes in opening and closing of stomata during the growing of nectarine fruit, by using a scanning electron microscope.
1. It was observed that the stomata on the fruit surfaces had not yet been differentiated at full bloom. During stage 1 of fruit growth, stomata development was rapid. Well-developed stomata on fruit surfaces were found abundantly in the equatorial areas of the fruit when fruitlet grew rapidly.
2. The density of the stomata on the fruit surfaces was highest on equatorial areas, intermediate in distal areas and lowest in proximal areas. There were no stomata in the suture zone.
3. The size of stomata was larger and they were well developed in proximal areas. The size of stomata seemed to be only slightly influenced by the surface expansion rate per unit area of fruit.
4. Diurnal changes in opening and closing of stomata in exposed and shaded fruitlets of nectarine indicated two peaks, one of which was in the day (10:00) and the other at midnight (22:00). The stomata were also open at both 14:00 and 22:00 in the dark-treated fruit. The stomatal aperture increased slightly in the evening and attained its maximum at midnight in the dark treatment. The degree of opening of stomata appeared to be related to changes in diurnal fruit growth. These results indicated that the stomata were open at midnight and in the case of the dark treatment, gases were exchanged through the opened stomata.
The existence of starch grains in guard cells on fruit surfaces suggested direct fixation CO₂ into organic acids and resynthesis of starch from the translocation of assimilation matter out of leaves to fruit during darkness.